stable door
noun
- the door of a stable, divided into two parts horizontally allowing one half to be shut and the other left open（上下两部分可以分别开关的）两截马厩门。
短语
shut （或bolt）the stable door after the horse has bolted
- try to avoid or prevent something bad or unwelcome when it is already too late to do so亡羊补牢, 为时晚矣。